This invention relates to new improved coated abrasive material. Coated abrasive material, which has been manufactured for many years and is commonly referred to as "sandpaper", is in general made by continuously applying to a suitable, relatively wide backing member, a first coat of an adhesive composition, referred to in the art as a "making" coat, followed by the immediate application of abrasive grains. The making coat is solidified to hold the grains on the backing member, after which, in most instances, an adhesive composition referred to as a "sand sizing" coat is applied and solidified. These coats constitute the bond for the abrasive grains, substantially all of which are bonded to the backing member only at their base so that they extend outwardly therefrom in cantilever fashion in random heights and spacings. After further cure of the adhesive bond, the coated abrasive material thus prepared is then processed into forms more suitable for use such as sheets, rolls, belts and discs.
The use of coated abrasive articles is occasioned, in general, with a relatively high initial rate of cut. However, during use, for various reasons, the rate of cut decreases and when it falls to a rate below economic usefulness the coated abrasive article is discarded.
Heretofore others have suggested incorporating a so-called "grinding aid" in the nature of an active filler in a coated abrasive product.
In recently issued U.S. Pat. No. 3,541,739 (Bryon et al) there is disclosed an active filler in at least the outermost layer which may be, for example, the supersize layer, which comprises, in addition to the filler, the usual coated abrasive bond material (e.g. resole phenolic resin) as a binder. Although other fillers may be included in such a composition, the most critical filler is disclosed to be a simple or complex metal halide, the latter being represented by, e.g., sodium fluoaluminate, i.e., cryolite, and potassium fluoborate (potassium borofluoride).
What one might term another species of "grinding aid" is disclosed in U.S. Pat. No. 3,256,076 (Duwell et al). The patentee therein discloses applying to the surface of a coated abrasive sheet material, as a supersize layer, a filmforming material which comprises an organic compound containing a chemically bound substituent which decomposes at the grinding temperature and which, in the presence of normal room humidity, is rapidly reactive with or corrosive to the metal being abraded. The chemically bound constituent is chlorine, bromine or divalent sulfur which on decomposition yields HCl, HBr, or H.sub.2 S. Such a reaction, according to the patentee, is indicated by a reduction in friction between the abrasive granules and the metal surface being abraded. One may conclude, it is believed, that this Duwell invention inhibits glazing by lowering the frictional forces in grinding thus lowering the grinding temperature.
U.S. Pat. No. 3,619,150 (Rinder et al) discloses a nonloading top coating for sandpaper particularly suited for sanding wood or painted surfaces. This coating consists of a metallic soap (e.g. zinc stearate) dispersed in a resin composition containing a mixture of a thermosetting resin and an elastomeric resin. The top coating does not contain an "active filler" grinding aid.
U.S. Pat. No. 3,232,729 (Holland et al) discloses a size coating (as distinguished from a supersize coating) containing a mineral filler (e.g. cryolite) on a sandpaper having a making coat of glue, hexanetriol and synthetic rubber latex (e.g. butadiene-styrene). The size coating can be made with animal glue or a thermosetting resin.
U.S. Pat. No. 3,331,667 (Schnabel) describes a maker coat and a size coat of a mixture of animal glue and a latex dispersion of a carboxylated styrene butadiene polymer. It contains no "active filler" grinding aid and this product seems to be primarily useful in the wood working industry.